The mechanics of stridulation of the cricketGryllus campestris

Summary Details in the stridulatory movement ofGryllus campestris were investigated using an improved high resolution miniature angle measurement system. The following results were obtained: During the closing (sound producing) stroke, the speed of the plectrum always has the same value (within measuring accuracy) at a given position. Plectrum speed is directly proportional to tooth spacing, which is known to vary along the file. The only exception to this rule were occasions when closing velocities of precisely 2 times the standard value were found. In between values were never recorded. While temperature has a large effect on the opening speed and duration, the closing speed has a very smallQ ₁₀ (0.07) which is equal to theQ ₁₀ of the resonance frequency of the harp. When the harps are removed, the proportionality between tooth spacing and scraper velocity is lost; the velocity is much increased (up to 3-fold) and the variance of the speed is enhanced 5-fold.These results are discussed with respect to 3 hypothetical models explaining the function of the sound generator system. The model describing the cricket sound generator as a clockwork with an escapement system is capable of accommodating all experimental data without any extra assumptions.     

Behavioral correlates of activity in identified hypocretin/orexin neurons

Micropipette recording with juxtacellular Neurobiotin ejection, linked micropipette-microwire recording, and antidromic and orthodromic activation from the ventral tegmental area and locus coeruleus were used to identify hypocretin (Hcrt) cells in anesthetized rats and develop criteria for identification of these cells in unanesthetized, unrestrained animals. We found that Hcrt cells have broad action potentials with elongated later positive deflections that distinguish them from adjacent antidromically identified cells. They are relatively inactive in quiet waking but are transiently activated during sensory stimulation. Hcrt cells are silent in slow wave sleep and tonic periods of REM sleep, with occasional burst discharge in phasic REM. Hcrt cells discharge in active waking and have moderate and approximately equal levels of activity during grooming and eating and maximal activity during exploratory behavior. Our findings suggest that these cells are activated during emotional and sensorimotor conditions similar to those that trigger cataplexy in narcoleptic animals.     

Ambient temperature modulates hypoxic-induced changes in rat body temperature and activity differentially

When rats, acclimated to an ambient temperature (T(a)) of 29 degrees C, are exposed to 10% O(2) for 63 h, the circadian rhythms of body temperature (T(b)) and level of activity (L(a)) are abolished, T(b) falls to a hypothermic nadir followed by a climb to a hyperthermic peak, L(a) remains depressed (Bishop B, Silva G, Krasney J, Salloum A, Roberts A, Nakano H, Shucard D, Rifkin D, and Farkas G. Am J Physiol Regulatory Integrative Comp Physiol 279: R1378-R1389, 2000), and overt brain pathology is detected (Krasney JA, Farkas G, Shucard DW, Salloum AC, Silva G, Roberts A, Rifkin D, Bishop B, and Rubio A. Soc Neurosci Abstr 25: 581, 1999). To determine the role of T(a) in these hypoxic-induced responses, T(b) and L(a) data were detected by telemetry every 15 min for 48 h on air, followed by 63 h on 10% O(2) from rats acclimated to 25 or 21 degrees C. Magnitudes and rates of decline in T(b) after onset of hypoxia were inversely proportional to T(a), whereas magnitudes and rates of T(b) climb after the hypothermic nadir were directly proportional to T(a). No hyperthermia, so prominent at 29 degrees C, occurred at 25 or 21 degrees C. The hypoxic depression of L(a) was least at 21 degrees C and persisted throughout the hypoxia. In contrast, T(a) was a strong determinant of the magnitudes and time courses of the initial fall and subsequent rise in T(b). We propose that the absence of hyperthermia at 21 and 25 degrees C as well as a persisting hypothermia may protect the brain from overt pathology.     

Fictive chewing activity in motor neurons and interneurons of the suboesophageal ganglion of Manduca sexta larvae

Alternating antiphasic rhythmic activity was observed in opener and closer mandibular motor neurons in the isolated suboesophageal ganglion of the larva of Manduca sexta (Lepidoptera: Sphingidae). This was interpreted provisionally as fictive chewing; the pattern is similar to that seen in semiintact animals but of lower frequency. Additionally, a variety of associated rhythmic activities were observed in suboesophageal interneurons. These could be classified into several different physiological types by their activity patterns in relation to the chewing cycle. Some of these neurons can modulate the rhythm when injected with current. It seems likely that they are part of or associated with a central pattern generator circuit for chewing.Abbreviations A anterior - CEC circumoesophageal connective - Cl-MN closer motor neuron - IN interneuron - MdN mandibular nerve - MN motor neuron - O-MN opener motor neuron     

Nonlinear activity of identified Lymnaea neurons

Two long-lasting discharges of action potentials were recorded from a buccal cell of the pond snail, respectively, before and after superfusing the preparation with low-calcium solution. The corresponding sequences of interspike intervals were then analysed by the nonlinear prediction methods. The results yield evidence of a small but clear nonlinearity only in the second of analysed tachograms. This finding is evaluated and discussed.     

Effects of weather and feeding on body temperature and activity in the snake Masticophis flagellum

1. 1.|Body temperature (T_b) and activity of the snake Masticophis flagellum were studied by radiotelemetry in an outdoor enclosure.

2. 2.|Mean diurnal T_b varied little over a wide range of weather conditions, but weather variation was accompanied by major changes in sun exposure and in the timing and duration of activity.

3. 3.|Recently fed snakes reduced activity and exhibited neither a thermophilic response nor increased precision of thermoregulation compared to fasting snakes.

Protein biosynthesis changes in Trypanosoma cruzi induced by supra-optimal temperature

Early during vertebrate infection, T. cruzi is exposed to the host blood at an elevated temperature. Bearing this in mind, the pattern of protein synthesis of two parasite forms was examined. SDS-PAGE of heated organisms showed an increase in at least four proteins (103, 92, 75 and 61 kD). The temperature effect is also manifested in cells whose RNA synthesis is reduced by actinomycin D treatment. The synthesis of the '29 degrees proteins' is inhibited at 40 degrees C in organisms growing in culture medium; when the organisms were maintained in serum, the inhibition was not observed. The inhibitory effect observed at 40 degrees C was reversed when the temperature was shifted to 29 degrees C. These proteins were synthesized for 180 min at 37 degrees C or 360 min at 40 degrees C. The increased protein synthesis manifested at 37 degrees C had decreased 45 min after the temperature was lowered to 29 degrees C. When the cells were pre-incubated at 40 degrees C and shifted to 29 degrees C, the synthesis of the heat-induced proteins proceeded for at least 180 min. This pattern of heat induction in epimastigotes and trypomastigotes is the same irrespective of whether the incubation medium is LIT (for epimastigotes), M-16 (for trypomastigotes), or when serum was used for both cell types.     

Effect of phosphatidylcholine on the body temperature and activity of posterior hypothalamus neurons in animals

The experiments on rats and rabbits have shown that exogenous phosphatidyl choline (PC) was capable of altering the body temperature and bioelectrical activity of posterior hypothalamus neurons following intravenous and intracerebroventricular administration. Intracerebroventricular PC was more effective in raising the body temperature of rats. The experiments on rabbits have demonstrated that the influence of PC (intravenous administration) on the body temperature depended on the initial body temperature. In rabbits, the changes in the impulse activity of certain non-thermosensitive posterior hypothalamus neurons induced by intracerebroventricular PC administration were found to be dependent on the initial firing rates. PC inhibited the increase in bioelectrical activity of thermosensitive neurons in posterior hypothalamus caused by the rise in the brain temperature secondary to body temperature elevation.     

Serotonin-immunoreactive neurons in the antennal lobes and suboesophageal ganglion of the honeybee

Summary We have used immunohistochemical methods to investigate the morphology of identified, presumptive serotonergic neurons in the antennal lobes and suboesophageal ganglion of the worker honeybee. A large interneuron (deutocerebral giant, DCG) is described that interconnects the deutocerebral antennal and dorsal lobes with the suboesophageal ganglion and descends into the ventral nerve chord. This neuron is accompanied by a second serotonin-immunoreactive interneuron with projections into the protocerebrum. Two pairs of bilateral immunoreactive serial homologues were identified in each of the three suboesophageal neuromeres and were also found in the thoracic ganglia. With the exception of the frontal commissure, no immunoreactive processes could be found in the peripheral nerves of the brain and the suboesophageal ganglion. The morphological studies on the serial homologues were extended by intracellular injections of Lucifer Yellow combined with immunofluorescence.     

Age-dependent behavioral changes and physiological changes in identified neurons in Aplysia californica

The gill withdrawal reflex (GWR) to direct gill stimulation was studied in sexually mature Aplysia and in those older by at least two months. The GWR threshold in old Aplysia was five- to sevenfold higher than that in mature animals. In the habituation paradigm, the GWR amplitude decremented rapidly to zero in old animals whereas in mature animals it persisted for at least ten trials. The GWR could not be dishabituated in old animals. The GWR is an age-dependent behavior in that parieto-visceral ganglion suppression of the GWR appears to increase with age. Also the electrophysiological properties of two neurons in the parieto-visceral ganglion were compared in the two age groups: L₇ a neuron which dishabituates the GWR in mature and not in old animals; and R₂ which manifests cytological changes with age. In old animals L₇′s input resistance was lower, the time constant was increased, and the size of the psp evoked by gill stimulation was smaller than those of mature L₇s. Similar membrane changes with age were measured in R₂. Soma size of L₇ was approximately the same in the two age groups as was that of R₂. The physiological parameters of neurons of known function continue to change during postmetamorphic life of Aplysia.     

Geographic variation in field body temperature of sceloporus lizards

1. Using data from the literature, I assessed how broad climatic patterns affected field body temperatures (T_b’s) of lizards in the genus Sceloporus.

2. Sceloporus at temperate latitudes had mean T_b’s of 35°C throughout their elevational range. This pattern is associated with “tropical” temperatures that extend into high north latitudes during the summer and the relatively low elevations occupied by the lizards.

3. At tropical latitudes, mean T_b declined from 35°C at low elevations to 31°C at high elevations. This pattern is associated with low seasonal variation in temperature at tropical latitudes and the relatively high elevations occupied by the lizards.     

Modulation of voltage-activated ion currents on identified neurons ofHelix pomatia L. by interleukin-1

1. The effect of interleukin-1 (IL-1) was studied on voltage-activated ion currents of the identified central neurons of Helix pomatia L. using a two-microelectrode voltage clamp. The voltage-activated inward current (ICa) was decreased, whereas the outward current (I(net) K) was increased by IL-1. 2. IL-1 affects both the transient and the delayed rectifying potassium currents. The IL-1 modulatory effect on the voltage-activated ion currents was voltage and dose dependent. The threshold concentration for IL-1 was 2 U/ml. 3. The proposed modulatory effect of IL-1 appears to have more than one site of action on the neuron membrane ion channels. 4. Rabbit anti-human IL-1 polyclonal antiserum eliminated the IL-1 effects on the voltage-activated inward and outward currents. This is the first report demonstrating a direct effect of IL-1 modulation of voltage-activated ion currents on neurons of mollusks.     

Characterization by immunocytochemistry of ionic channels in Helix aspersa suboesophageal brain ganglia neurons

The aim of this work was to characterize several ionic channels in nervous cells of the suboesophageal visceral, left and right parietal, and left and right pleural brain ganglia complex of the snail Helix aspersa by immunocytochemistry. We have studied the immunostaining reaction for a wide panel of eleven polyclonal antibodies raised against mammal antigens as follows: voltage-gated-Na+ channel; voltage-gated-delayed-rectifier-K+ channel; SK2-small-conductance-Ca2+-dependent-K+ channel apamin sensitive; SK3 potassium channel; charybdotoxin-sensitive voltage-dependent potassium channel; BKCa-maxi-conductance-Ca2+-dependent-K+ channel; hyperpolarization-activated cyclic nucleotide-gated potassium channel 4; G-protein-activated inwardly rectifying potassium channel GIRK2 and voltage-gated-calcium of L, N and P/Q type channels. Our results show positive reaction in neurons, but neither in glia cells nor in processes in the Helix suboesophageal ganglia. Our results suggest the occurrence of molecules in Helix neurons sharing antigenic determinants with mammal ionic channels. The reaction density and distribution of immunoreactive staining within neurons is specific for each one of the antisera tested. The studies of co-localization of immunoreaction, on alternate serial sections of the anterior right parietal ganglion, have shown for several recognized mapped neurons that they can simultaneously be expressed among two and seven different ionic protein channels. These results are considered a key structural support for the interpretation of Helix aspersa neuron electrophysiological activity.     

Skin temperature changes in humans induced by local peripheral cooling

Local peripheral cooling (immerson of legs up to the knees into 12°C water) increased heart rate and blood pressure by 10–20% within the first 3–10 min of cooling. During further cooling heart rate remained elevated, while systolic and diastolic blood pressures decreased to the control value. Data on heart rate indicate a permanent activation of the sympathetic nervous system during local cooling.Skin temperatures (measured topically by thermosensors) decreased on some non-cooled areas of the body (fingers, palms and thighs) immediately after the start of local cooling. On the other hand, skin temperatures on chest and forehead were not influenced. During cooling skin temperatures on thighs remained low, but skin temperatures on fingers tended to increase. Changes in skin temperatures on non-cooled areas of the body indicate that a permanent and generalized activation of the sympathetic nervous system occurs during local cooling.Cold induced cycles of vasodilation (CIVD) were observed on fingers, palms and forearms during local cooling. Minute cycles in skin temperatures were observed on forehead, thighs and chest. Minute cycles coincided with those in the heart rate, indicating a permanent, generalized but discontinuous control of vasomotion by the sympathetic nervous system during local cooling.Infrared thermographic recordings from different body areas indicated that local peripheral cooling lowered skin temperatures in all areas of the body within 5 min. Distant areas of the body (extremities) and pectoral muscles showed greater hypothermia than abdominal areas and head. After 10 min of cooling average skin temperatures in all areas of the body returned to the original level and further fluctuated at approximately 10–15 min intervals.Data indicate that during local cooling skin blood flow in all areas of the body surface permanently fluctuates forming a mosaic of dynamic changes in skin temperatures. Since tympanic temperature increases, while skin temperature decreases immediately after the start of the local cooling, it appears that the initial vasoconstrictor response is being controlled independently of the central temperature input.     

Modulation of TRPA1 channel activity by Cdk5 in sensory neurons

Transient receptor potential cation channel, subfamily A, member 1 (TRPA1), is activated by a broad range of noxious stimuli. Cdk5, a member of the Cdk family, has recently been identified as a modulator of pain signaling pathways. In the current study, we investigated the extent to which Cdk5 modulates TRPA1 activity. Cdk5 inhibition was found to attenuate TRPA1 response to agonist in mouse DRG sensory neurons. Additionally, the presence of active Cdk5 was associated with increased TRPA1 phosphorylation in transfected HEK293 cells that was roscovitine-sensitive and absent in the mouse mutant S449A full-length channel. Immunopurified Cdk5 was observed to phosphorylate human TRPA1 peptide substrate at S448A in vitro. Our results point to a role for Cdk5 in modulating TRPA1 activity.